Azazel

A demonic-looking mutant and leader of the Neyaphem, Azazel was banished to a dimensional void due to his appearance. Becoming bitter at what he considered "Normal-looking" mutants, Azazel began fathering children with mutants bearing strange appearances, one of whom would become Nightcrawler, as a part of his overall plan to escape the void. He would clash with the X-Men over his plans before eventually being defeated and re-banished.